1. Field of the Invention
The present invention relates to a base station, a radio communication system, and a communication method.
2. Description of the Related Art
There has been recent demand for radio communication systems with multimedia services. It has been thought that suitable control with consideration for a different Quality of Service (hereafter, referred to as ‘QoS’) for each application will be indispensable in the future. The requirements for traffic characteristics and networks specified by the QoS differ according to the type of application. As a result, in order to satisfy the requirements for QoS of each application used by mobile stations, it has been thought that constructing networks and control technologies with consideration for the QoS are essential.
Furthermore, it has been thought that Internet protocol (IP) may be used as the protocol for all routes between a transmission side and a reception side, in future network systems. As a result, there is a high possibility that radio communication systems conventionally constructed by using their own networks may be converted to IP-based systems. Packet communication is fundamental to IP-based systems.
Therefore, it is necessary for the radio communication systems to control for QoS in packet communication. In this case, reception quality in a mobile station always varies according to interference caused by variation of Propagation path environment or other signals, in the radio communication systems. As a result, special consideration, which is different from that for wired communication systems, is required. From such background, various control technologies regarding QoS in the radio communication systems have been proposed. In addition, methods of scheduling to determine transmission order with consideration for fairness among mobile stations not requesting any QoS have been proposed.
For example, as a control technology for an environment where mobile stations not requesting any QoS and mobile stations requesting QoS coexist, a method has been proposed for scheduling by classifying the mobile stations into mobile stations requesting QoS and mobile stations not requesting any QoS, and further classifying the mobile stations requesting QoS into a QoS critical group requiring a high level of QoS and a QoS non-critical group requiring a low level of QoS (e.g., Synopsis of Institute of Electronics, Information, and Communication Engineers Society Convention 2002, ‘All-IP MOBILE NETWORK ARCHITECTURE PROPOSAL (5), QoS GUARANTEE PACKET SCHEDULER FOR BASE STATION’ written by Ono et al., Institute of Electronics, Information, and Communication Engineers, p. 408, September 2002). With this method, the transmission order is controlled such that packets transmitted to the mobile stations in the QoS critical group and packets transmitted to the mobile stations having actual values for QoS, which are lower than the request value, are given higher priorities.
However, conventionally proposed control technologies have not controlled with consideration for the case where various mobile stations, such as mobile stations not requesting any predetermined QoS or any specific Request values for communication quality, mobile stations requesting only predetermined QoS, and mobile stations requesting specific request values for communication quality, coexist within the radio communication system. Accordingly, packet transmission between the base station and a plurality of mobile stations has not been appropriately controlled. As a result, appropriate services have not been provided for all mobile stations. For example, there are cases where the request value for communication quality in a certain mobile station have not been satisfied, utilization efficiency of radio resources has been lowered due to assignment of excess radio resources to a mobile station requesting a certain class of QoS, or communication quality of a certain mobile station has extremely degraded. These are problems when the radio communication systems provide a certain quality of service. The scheduling methods described in the above-mentioned literature could not sufficiently guarantee QoS.
Furthermore, since the present Internet is an open network that communicates using TCP/IP, various packets are transferred from multiple hosts on the network. Accordingly, it is assumed that the method of handling various packets will become a very important problem when the radio communication systems are converted to IP-based systems in the future.